System for packaging



June 1966 F. M. FERRELL SYSTEM FOR PACKAGING Filed Aug. 25. 1963 tions.

United States Patent 3,255,020 SYSTEM FOR PACKAGING Frank M. Ferrell,Wilmington, Del., assiguor to Air Prod-.

nets and Chemicals, Inc., Philadelphia, Pa., a corpora- This inventionrelates to a system for packaging goods which are desirably stored undernon-oxidizing condi- Heretofore there have been systems in which aninert gas was included in a package containing goods sensitive to thepresence of oxygen. As explained in British Patent 734,197, a watersynthesis catalyst can be included in a package containing an inert gasand a minor amount of hydrogen adapted to react with the trace amountsof oxygen for enhancing the preservation effectiveness of the inert gas.Rosenblatt 2,582,885 describes one form of water synthesis'catalystadapted to remove trace amounts of oxygen from technical grades ofnitrogen by combustion of the hydrogen introduced for such purification.Lindewald 2,789,059 describes one system whereby an inert gas in awarehouse may be maintained by circulating a mixture of inert gas andhydrogen through a catalytic zone for water synthesis.

In accordance with the present invention, particles of water synthesiscatalyst having a particle size within the range from about 1millimicron to about 500 microns are positioned between a plastic sheetfunctioning as gas permeable membrane exposed to the internal portion ofthe package and a gas impermeable sheet such as aluminum foil or glycolterephthalate film. The gas permeable plastic sheet serves to protectthe goods from contact with the catalyst. Such shielded, finely dividedparticles of water synthesis catalyst remove trace amounts of oxygenfrom the packaging gas of the present invention which packaging gas is amixture consisting of from about 95% to about 97% cryogenically purifiednitrogen and not less than 3% nor more than 5% hydrogen by volume. Bythe present invention, the danger of accidental fire during the fillingor opening of the package is eliminated notwithstanding the well-knownflammability of mixtures of air and hydrogen.

When a package containing a mixture of nitrogen and hydrogen is opened,the hydrogen gas and the catalyst for synthesizing water are exposed toatmospheric oxygen. If the quantity of hydrogen in the nitrogen-hydrogenmixture is excessive, a fire and/ or explosion hazard could result fromthe exposure of air and hydrogen to the water synthesis catalyst. Animportant advantage of the gas mixture of the present invention is thenon-flammability of the gas mixture resulting from mixtures of air with95 nitrogen, 5% hydrogen in any proportion.

The establishment of 5% as the maximum hydrogen content permissiblewithout encountering a flammability hazard helps to transform hydrogenas a packaging gas from a frightening theory to a commerciallyattractive practice. The well-known explosion hazards connected with theuse of gaseous hydrogen in factories has tended to prompt managers ofplants packaging food under inert gas to dismiss the proposal of usinghydrogen as merely of theoretical interest. However, the assurance ofthe non-flammability of plausible mixtures of air and the hydrogencontaining inert gas of the present invention overcomes this otherwiseinsurmountable obstacle.

By a series of tests it is established that if the hydrogenconcentration is insuflicient, the probability of prompt conversion ofoxygen to water is significantly reduced. Although only two volumes ofhydrogen per volume of 3,255,026 Patented June 7, 1966 "Ice oxygen aretheoretically necessary, reliable minimizing of the oxygen content ofthe inert gas requires a hydrogen to oxygen ratio of at least 3.to l inaccordance with the present invention. Because some goods preferentiallysorb relatively large amounts of oxygen, and because the volume of inertgas ordinarily employed in consumer packages is relatively small, the 3to 1 minimum ratio of hydrogen to conceivable maximum oxygenconcentration sometimes necessitates the redesign of the package toprovide a larger volume of inert gas than was previously conventional.Any massive puncturing of the sealing of the package destroys thestorage stability of the package, but the 3 to 1 ratio requirement and5% hydrogen permits tiny leaks of air into the inert gas over aprolonged period without permitting the goods to undergo oxidativedegeneration. Hydrogen tends to leak preferentially from any such tinyleaks, so the probabilities of successful preservation are enhanced bythe use of a gas mixture containing the preferred 5% hydrogen instead ofa lower concentration.

Particular attention is directed to the feature of employingcryogenically purified nitrogen. In some previous inert gas systems,carbon dioxide has been employed either alone or as a component of a gasconsisting predominantly of nitrogen and derived from flue gas. In thedevelopment of the present invention, the surprising discovery was madethat trace components in such modi fied flue gas tend to impair theusefulness of a system for storage of foods, seeds, tobacco, etc., andthatgreater reliability of retention of flavor and other diflicultymeasured properties was achieved using cryogenically purified nitrogenas the inert gas. In archives, and/or warehouses employing inert gasmerely for fire protection, nitrogen derived from flue gas might becheaper and hence the preferred inert gas for admixture with a minoramount of hydrogen for circulation through a water syn thesis catalyst.However, in accordance with the present invention, cryogenicallypurified nitrogen is employed (in admixture with from about 3% to 5% byvolume hydrogen) as the inert gas in a package containing watersynthesis catalyst which is finely divided and shielded by a permeableplastic film and such feature enhances the reliability of the packagingfor features such as flavor retention. Just what are the tracecomponents present in inert gas derived by purification of flue gas butabsent from cryogenically purified nitrogen is not known, but carbondioxide is deemed more likely troublesome than bacteria, dust, moisture,or related contaminants. Cryogenically purified nitrogen is only atechnical grade, and contains Whateveramounts of argon, helium, etc.,are not profitably salvaged during the production of nitrogen. Asignificant portion of the cryogenically purified nitrogen is routinelyprocessed over a Water synthesis catalyst to lower the oxygenconcentration to less than 1 p.p.m.', but because the present inventionemploys a Water synthesis catalyst, the inert gas can include the 'traceamounts of oxygen resulting from commercial nitrogen production.

The nature of the invention is further clarified by reference to theaccompanying drawings. In the drawings, FIGURE 1 schematically shows aplastic bag 10 containing goods 11 (e.g., powdered milk) and a gasmixture consisting essentially of'cryogenically purified nitrogen andabout 4% hydrogen. FIGURE 2 is a cross-section taken along line 22 ofFIG. 1 of a segment of the thickness of the bag 10, and shows an outersheet of a gas impermeable material 12, a gas permeable sheet 13 at theinside of the package, and finely divided particles of water synthesiscatalyst 14 interposed therebetween. At at least some zones, the innersheet 13 is bonded to the outer sheet 12 at bonding zones 15.

Examples of sheet materials suitable as the gas impermeable sheet 12include aluminum foil, plastic laminates having aluminum cores, and 10mil films of glycol terephthalate. Examples of gas permeable film 13include 2 mil polyethylene, thin polyvinylalcohol and thinpolyvinylacetate. The catalyst particles 14 can be secured to at leastone of the two sheet materials of a flexible package by means of anadhesive such as varnish or by mechanical means.

It is often desirable to secure the catalyst particles to a sheetmaterial by employing the catalyst particles as the thickener for an inkprinted onto a sheet material. If desired, the sorptive carrierparticles may be adhered to one of the films prior to the impregnationof the solution of the compound of the noble metal functioning as thewater synthesis catalyst into the sorptive carrier. As shown in thedrawing, a somewhat quilted structure may be provided so that thecatalyst particles are secured to zones spaced from each other, wherebyportions of the bonding zones 15 securing the gas permeable film to theopposing face of the sandwich are at spaced locations. If desired, thecatalyst particles 14 can be printed uniformly onto the permeable film13 which can be adhered to the nonpermeable sheet 12 without any plannedunbonded areas. The readiness with which the hydrogen and oxygen diffusethrough a thin permeable plastic film is so great that only a few mills(tenths of a cent) worth of catalyst can sufiice even when the catalystparticles are embedded between the lamina of the sandwich. Even lowercatalyst costs are generally achieved by the spaced lines of bondingzones 15 of the quilted structure shown schematically in FIGURE 2. Ifdesired, the catalyst particles 14 and permeable sheet 13 can bepositioned merely near the top of the bag adjacent to the normallocation of the hydrogen-containing-nitrogen.

The invention may be further clarified by reference to the followingexample:

EXAMPLE I A small package of powdered milk comprises a bag formed fromaluminum foil. Particular attention is directed to the gas permeablesheet of polyethylene bonded in quilt-like fashion to the aluminum foil,thus defining a plurality of small compartments spaced from each other.In each compartment, a small amount of finely pulverized water synthesiscatalyst consisting of 0.1% palladium on sorptive alumina is positionedin such a way as to be effective as a water synthesis catalyst. Thesorptive eta alumina particles are prepared by dehydration of highpurity beta alumina trihydrate. Eta alumina particles within the sizerange from 200 microns to 400 microns are partially embedded intoheatsoftened film of 2 mil polyethylene. ,The thus adhered particles arespaced zones of a checkerboard embossed film. The particle areimpregnated with an aqueous solution of chloropalladic acid, dried undervacuum, and treated with hydrogen. The polyethylene sheet having theadhered particles of palladium on eta alumina is adhered to thealunminum foil at the gridiron pattern lines, and the thus preparedsandwich structure is fabricated into a bag. The bag is filled with themixture of 95% cryogenically purified nitrogen and hydrogen, andadvanced through a filling machine in which powdered milk displaces mostof the gas, and the package is sealed. After storage for several months,tests on randomly selected packages establish the absence of oxygen andthe presence of hydrogen in the gas in the package. Moreover, the flavorretention for the powdered milk is excellent for such prolonged storage.

EXAMPLE II An apparatus is set up for evaluating gas permeable membranesand/or water synthesis catalysts. A gas stant temperature zone, and thenthrough an oxygen detection zone comprising a bed of eta alumina pelletsimpregnated with about 5% palladium, and equipped with thermocouples fordetecting any temperature increase. By a series of tests it is shownthat each of palladium and platinum catalyze at ambient temperatures theflamless reaction of 0.5% oxygen in a gas mixture comprising about 4.5%hydrogen and nitrogen, but that certain other oxidation catalysts areeffective only at higher temperatures. At a concentration within therange from about 0.1% to 1%, palladium and/or platinum are effective ona variety of sorptive supports, including alumina and silica. By aseries of tests it is established that the particle size must be withinthe range from 1 millimicron to 500 microns for the reliable catalyticeffectiveness for cooperation with flexible film of gas permeablemembrane. For example, the weight of a 10 mm. head of silica impregnatedwith 0.1% palladium is great enough that during shifting of a packageduring shipment, the bonding of a gas permeable film to an outer sheetmight be broken, whereas the smaller Weight of the tiny catalystparticles of the present invention imposes no such strain during thelurching of cargo. Particles too small in size are not readilypositioned between the walls of a multi-wall bag. Particles smaller thanabout 10 microns would ordinarily be less advantageous than particles ofthe 10500 micron range, but particles as small as l millimicron aredeemed to have some suitability as water synthesis catalysts.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

The invention claimed is as follows:

1. A consumer package of food protected from loss of flavor by apackaging gas, said packaging gas being prepared by cryogenicallypurifying nitrogen, and adding a minor amount of hydrogen thereto toprovide a mixture consisting of not less than 3% nor more than 5%hydrogen and from 95% to 97% cryogenically purified nitrogen, said gasbeing confined in contact with the food by gas impermeable sheetmaterial imparting structural strength to the package; catalystparticles consisting ofa sorptive carrier and from 0.1% to 1% noblemetal ofthe group consisting of palladium, platinum and mixtures thereofdeposited in said sorptive carrier, said particles having a size rangefrom about 200 to about 400 microns; a thin film of plastic protectingsaid catalyst particles from contact with the food, said thin film beingbonded to the inner surface of the gas impermeable sheet at spacedbonding zones defining small compartments for said catalyst particles,whereby each catalyst particle is maintained within its smallcompartment even during lurching of the food package duringtransportation thereof, said thin plastic film permitting the diffusionof oxygen, nitrogen and hydrogen to, from and between the zone adjacentthe catalyst particles and the zone adjacent the food, whereby anyresidual oxygen sorbed on the packaged food diffuses to the catalystparticle for conversion to water vapor.

2. In the method of protecting the flavor of food by packaging the foodin a consumer package containing both a water synthesis catalyst and ahydrogen containing gas, the improvement which consists of: employingnot less than 3% nor more than 5% hydrogen in the gas sealed in thepackage; employing a volume ratio of hydrogen to expected oxygen of atleast 3 to 1 such 'oxygen comprising oxygen sorbed on the packaged food;cryogenically purifying nitrogen to provide the inert gas constituting95 to 97% of the gas sealed in the package; employing particles of watersynthesis catalyst 'Within the size range from about 200 to about 400microns, said catalyst particles consisting of a sorptive carrier andfrom 0.1% to 1% noble metal of the group consisting of palladiumplatinum and mixtures thereof deposited in said sorptive carrier; andshielding the Water synthesis catalyst particles from the food bypositioning such catalyst particles in small compartments defined by thespaced bonding zones securing a thin gas permeable plastic film to theinner surface of the structurally strong sheet of gas impermeablematerial of said package, whereby each catalyst particle is maintainedwithin its small compartment even during lurching of the food packageduring transportation thereof, said thin plastic film permitting thediffusion of oxygen, nitrogen and hydrogen to, from and between the zoneadjacent the catalyst particles and the zone adjacent the food, wherebyany residual oxygen sorbed on the packaged food diffuses to the catalystparticle for conversion to Water vapor.

References Cited by the Examiner UNITED STATES PATENTS Boesel 312-311Sarge et al. 31231 X Rosenblatt 232.1

Eustis 20684 Lindewald 99-189 Selby et a1. 206-46 Adler 31231 Beaumont99189 X THERON E. CONDON, Primary Examiner.

GEORGE O. RALSTON, Examiner.

J. M. CASKIE, Assistant Examiner.

1. A CONSUMER PACKAGE OF FOOD ROTECTED FROM LOSS OF FLAVOR BY APACKAGING GAS, SAID PACKAGING GAS BEING PREPARED BY CRYOGENICALLYPURIFYING NITROGEN, AND ADDING A MINOR AMOUNT OF HYDROGEN THERETO TOPROVIDE A MIXTURE CONSISTING OF NOT LESS THAN 3% NOR MORE THAN 5%HYDROGEN AND FROM 95% TO 97% CRYOGENICALLY PURIFIED NITROGEN, SAID GASBEING CONFINED IN CONTACT WITH THE FOOD BY GAS IMPERMEABLE SHEETMATERIAL IMPARTING STRUCTURAL STRENGTH TO THE PACKAGE; CATALYSTPARTICLES CONSISTING OF A SORPTIVE CARRIER AND FROM 0.1% TO 1% NOBLEMETAL OF THE GROUP CONSISTING OF PALLADIUM, PLATINUM AND MIXTURESTHEREOF DEPOSITED IN SAID SORPTIVE CARRIER, SAID PARTICLES HAVING A SIZERANGE FROM ABOUT 200 TO ABOUT 400 MICRONS; A THIN FILM OF PLASTICPROTECTING SAID CATALYST PARTICLES FROM CONTACT WITH THE FOOD, SAID THINFILM BEING BONDED TO THE INNER SURFACE OF THE GAS IMPERMEABLE SHEET ATSPACED BONDING ZONES DEFINING SMALL COMPARTMENTS FOR SAID CATALYSTPARTICLES, WHEREBY EACH CATALYST PARTICLE IS MAINTAINED WITHIN ITS SMALLCOMPARTMENT EVEN DURING LURCHING OF THE FOOD PACKAGE DURINGTRANSPORTATION THEREOF, SAID THIN PLASTIC FILM PERMITTING THE DIFFUSIONOF OXYGEN, NITROGEN AND HYDROGEN TO, FROM AND BETWEEN THE ZONE ADJACENTTHE CATALYST PARTICLES AND THE ZONE ADJACENT THE FOOD, WHEREBY ANYRESIDUAL OXYGEN SORBED ON THE PACKAGED FOOD DIFFUSES TO THE CATALYSTPARTICLE FOR CONVERSION TO WATER VAPOR.